Cancers with less than 40,000 cases diagnosed per year in the U.S. are both an unmet medical need and unparalleled opportunity. Rare cancers have been the basis of paradigm-defining concepts in cancer because their rarity comes from the limited combinations of events that result in that particular type of cancer. For example, the first instance of a translocation driven oncogenic event, BRC-ABL, was discovered in seven cases of chronic myelogenous leukemia. Nowell P C & D A Hungerford, A minute chromosome in human chronic granulocytic leukemia, Science (142) 1497 (1960). The role of tumor suppressors, particularly p53 and RB1, was found through the investigation of tumors from patients with Li-Fraumeni syndrome and familial retinoblastoma, respectively. As researchers find necessary and sufficient genetic changes that drive rare cancers, these can be further studied to understand and treat more common cancers. If researchers can identify what core cancer pathways are operational in a rare tumor, the knowledge about those pathways from more common cancers can be leveraged to improve diagnosis and treatment.
Adrenocortical carcinoma (ACC) is an aggressive cancer of the adrenal cortex. Recent studies show that the outcome for ACC patients has remained unchanged in the past 25 years, with a 40% overall 5-year survival rate of patients undergoing surgical resection. K Y Bilimoria et al., Adrenocortical carcinoma in the United States: treatment utilization and prognostic factors, Cancer (113) 3130-3136 (2008). ACC is rare with an incidence of approximately 300 new cases per year in the United States. Id. The rarity of ACC suggests either a specific genomic alteration, or a small number of alterations, is necessary and sufficient for tumor development. Childhood ACC is a feature of the Li-Fraumeni syndrome and mutation of p53, but inactivating mutations in p53 are an uncommon feature of adult ACC. R. Libe et al., Somatic TP53 mutations are relatively rare among adrenocortical cancers with the frequent 17p13 loss of heterozygosity, Clinical Cancer Res. (13) 844-850 (2007). Comparative genomic hybridization studies demonstrate that no abnormality has been seen in more than 60% of ACCs examined. Bussey K J & M J Demeure, Genomic and expression profiling of adrenocortical carcinoma: application to diagnosis, prognosis and treatment, Future Oncol. (5) 641-655 (2009). This implies that the necessary and sufficient alteration(s) responsible for the pathogenesis of ACC exist either below the limit of detection or resolution of previously used technologies and/or result from structural events that do not consistently alter copy number. It could also imply that there is genomic heterogeneity that converges on a small number of critical pathways resulting in this rare disease.
ACC patients who present clinically with large, locally invasive tumors, have involved margins or present with metastatic disease, fare considerably worse with 5 year survival rates of 10-20%, largely due to the limited effectiveness of chemotherapy. The only realistic opportunity for cure is a complete surgical resection. Unfortunately, metastatic spread is already present in 40-70% of patients at the time of diagnosis precluding cure. Standard chemotherapy in ACC cases remains based on mitotane which was first approved in 1960. Mitotane, also known as o,p′-DDD, is a derivative of the pesticide DDT and an adrenolytic. Tacon, L. J. et al., Current and emerging therapies for advanced adrenocortical carcinoma. Oncologist (16) 36-48 (2011); Daffara, F. et al., Prospective evaluation of mitotane toxicity in adrenocortical cancer patients treated adjuvantly Endocr. Relat. Cancer (15) 1043-53 (2008); Netto, A. D. et al., Treatment of Adrenocortical Cancer with O,P′-Ddd. Ann. Intern. Med. (59) 74-78 (1963); and Bapat, A. A. et al., A fly in the ointment: reassessing mitotane's role in the treatment of adrenocortical carcinoma. Pharmacogenomics (13) 1207-1209 (2012). The response rates to mitotane as a single agent is a relatively poor 23%, but survival for those patients whose tumors do respond is improved from 14 to 50 months. Tacon, L. J. et al., Current and emerging therapies for advanced adrenocortical carcinoma. Oncologist (16) 36-48 (2011); Daffara, F. et al., Prospective evaluation of mitotane toxicity in adrenocortical cancer patients treated adjuvantly. Endocr. Relat. Cancer, (15) 1043-53 (2008); and Netto, A. D. et al., Treatment of Adrenocortical Cancer with O,P′-Ddd. Ann. Intern. Med. (59) 74-78 (1963). Mitotane is most often used in combination with etoposide, doxorubicin, and cisplatin (EDP-M) based on the reported 49% response rate in a phase II trial. Berruti, A. et al., Etoposide, doxorubicin and cisplatin plus mitotane in the treatment of advanced adrenocortical carcinoma: a large prospective phase II trial Endocr. Relat. Cancer. (12) 657-666 (2005). However, further study in the phase III FIRM-ACT trial demonstrated the response rate to EDP-M was 23.2% and the median progression-free survival interval was 5 months. Fassnacht, M. et al., Combination Chemotherapy in Advanced Adrenocortical Carcinoma. N. Engl. J. Med. (366) 2189-2197 (2012). For most patients, mitotane is poorly tolerated due to its severe toxic side effects, including obliteration of the healthy contralateral adrenal gland. There is no approved second-line regimen for those whose disease progresses on these agents.
The increased incidence of ACC in patients with Li-Fraumeni syndrome suggests the p53 pathway is involved in ACC progression. Fassnacht, M. et al., Adrenocortical carcinoma: a clinician's update Nat. Rev. Endocrinol. (7) 323-335 (2011). In adults, however, mutation in p53 is seen in less than 25% of cases suggesting that other elements of the p53 pathway may be perturbed. Waldmann, J. et al., Clinical impact of TP53 alterations in adrenocortical carcinomas Langenbecks Arch. Surg. (397) 209-216 (2012); Libe, R. et al., Somatic TP53 mutations are relatively rare among adrenocortical cancers with the frequent 17p13 loss of heterozygosity Clin. Cancer Res. (13) 844-850 (2007); and Hamid, T. and S. S. Kakar, PTTG/securin activates expression of p53 and modulates its function Mol. Cancer (3) 18 (2004). It has been found that p53 is a major driver of differential gene expression when comparing ACC to normal adrenal glands or when comparing low and high-grade tumors. Demeure, M. J. et al., PTTG1 overexpression in adrenocortical cancer is associated with poor survival and represents a potential therapeutic target Surgery (154) 1405-1416 (2013). This dysregulation is accompanied by perturbations in the G2/M transition of the cell cycle. Demeure, M. J. et al., PTTG1 overexpression in adrenocortical cancer is associated with poor survival and represents a potential therapeutic target Surgery (154) 1405-1416 (2013). Moreover, Polo-like kinase 1 (PLK-1) negatively modulates p53 functioning, promotes Mouse double minute 2 (MDM2) activity through its phosphorylation, and is involved in the G2/M transition. X. Liu et al., Polo-like Kinase (Plk)1 depletion induces apoptosis in cancer cells, Proc. Nat. Acad. Sci. (100) 5789-5794 (2003).
p53 is a tumor suppressor and transcription factor that responds to cellular stress by activating the transcription of numerous genes involved in cell cycle arrest, apoptosis, senescence, and DNA repair. Unlike normal cells, which have infrequent cause for p53 activation, tumor cells are under constant cellular stress from various insults including hypoxia and pro-apoptotic oncogene activation. Thus, there is a strong selective advantage for inactivation of the p53 pathway in tumors, eliminating p53 function may be a prerequisite for tumor survival. Mouse models have been used to demonstrate that absence of p53 function is a continuous requirement for the maintenance of established tumors; when p53 function is restored to tumors with inactivated p53, the tumors regressed.
p53 is inactivated by mutation and/or loss in 50% of solid tumors and 10% of liquid tumors. Other key members of the p53 pathway are also genetically or epigenetically altered in cancer. MDM2, an oncoprotein, inhibits p53 function, and it is activated by gene amplification at incidence rates that are reported to be as high as 10%. MDM2, in turn, is inhibited by another tumor suppressor, p14ARF. Alterations downstream of p53 may be responsible for at least partially inactivating the p53 pathway in p53 wild type tumors (p53WT). In support of this concept, some p53WT tumors appear to exhibit reduced apoptotic capacity, although their capacity to undergo cell cycle arrest remains intact. MDM2 inhibits p53 activity by three mechanisms: 1) acting as an E3 ubiquitin ligase to promote p53 degradation; 2) binding to and blocking the p53 transcriptional activation domain; and 3) exporting p53 from the nucleus to the cytoplasm.
Apoptosis is an active form of cell death that is involved in multiple processes of normal cell development as well as in malignant cell transformations. Mechanism of apoptosis is engaged in biological events induced by various types of drugs, cytokines, and growth factors, oxidative stress, radiation, aging, autoimmune diseases, and immune rejection within organ transplantation. Recent studies on apoptosis demonstrate that common molecular mechanisms are employed in various types of apoptosis, induced by hormones, cytokines, growth factor deprivation, chemotherapeutic agents, ionizing radiation, immunological disorders, AIDS, cancer and aging.
Cascade-like activation of caspase proteases represents a point in the induction of apoptosis. Two types of apoptosis signaling mediated by the caspase cascade have been described: receptor-dependent and receptor-independent. The initial phase of receptor-depending triggering of apoptosis includes activation of appropriate death receptors by specific ligands, such as TNF or FasL, which are presently the most studied inductors of apoptosis. Upon activation, cell surface death receptors, Fas (CD95) or TNFR1, are attached to cytosolic adapter proteins (FADD, MORT, RIP, TRADD), which in turn recruit caspase-8 to activate the interleukin-1-β-converting enzyme ICE/CED-3 family caspase cascade, followed by activation of CPP32/caspase-3-subfamily of cysteine proteases, whose members are localized in the cytoplasm in the form of latent precursors known as procaspases. Receptor-independent types of caspase cascade-mediated apoptosis usually include important cytochrome c-inducible mechanism that requires the formation of tertiary complex of cytochrome c, dATP, Apaf-1 and procaspase-9, which lead to the activation of the latter via autoproteolysis and homodimerization, and subsequent caspase cascade activation. See D. R. McIlwain et al. Caspase Functions in Cell Death and Disease Cold Spring Harbor Perspectives in Biology (5) a008656 (2013). In general, caspases involved in mediating apoptosis have been generally divided by function: (i) initiator caspases (i.e., caspases 8 and 9) and (ii) executioner caspases (i.e., caspases 3, 6, and 7).
Restoring cell death functionality as a therapy for cancers of the endocrine system, including ACC, is a desirable strategy, as many current therapies rely on use of the apoptosis-inducing caspase cascade. Apoptosis-inducing mechanisms in patients with different cancers, however, may not properly function, which may lead to poor patient responses to one or more therapeutics. Embodiments of the present invention provide methods that can overcome at least some of these shortcomings in the therapeutic-strategy field. The present invention provides methods of treatment that can be tailored by determining which, if any caspases, are expressed and/or methods of the present invention can be applied as a clinical assay to guide treatment decisions. Some aspects of the invention may also function as a screening model to identify new therapies with alternative modes of cellular death.
The articles, treatises, patents, references, and published patent applications described above and herein are hereby incorporated by reference in their entirety for all purposes.